Caerulein is a decapeptide which has been discovered in the skin of an Australian amphibian, Hyla caerulea, of which the chemical structure resembles that of cholecystokinin, and stimulates contraction of the gallbladder, secretion of the pancreatic juice, motion of the intestine, and secretion of the gastric juice. The complete structure of caerulein has been elucidated, and the chemically synthetic route has also been established. [A. Anastasi, V. Erspamer and R. Endean, Experientia, 23, 699 (1967); L. Bernardi, G. Bosisio, R. de Castiglione and O. Goffredo, Ibid., 23, 700; V. Erspamer, G. Bertaccini, G. de Caro, R. Endean and M. Impicciatore, Ibid., 23, 702].
The chemical name of caerulein is: 5-oxo-L-prolyl-L-glutaminyl-L-aspartyl-O-sulfo-L-tryosyl-L-threonylglycyl- L-tryptophyl-L-methionyl-L-aspartyl-L-phenylalaninamide.
The toxicity of caerulein has been investigated in detail [Chieli, T. et al., Toxico, and Pharmaco., 23, 480 (1972); Miyazaki et al., Kiso to Rinsho in Japan, 8, no. 7, 98 (1974)]; acute toxicity in mice (intravenous), LD.sub.50 =647 mg/kg in male and 702 mg/kg in female; in rats (intravenous), LD.sub.50 =714 mg/kg in male and 571 mg/kg in female.